Explanation:

Solution:
Efficiency (A : B) =150:100= 3 : 2 then days 2:3
B takes 21 days to do the work. Then A takes 14 days to do the work.
(3 === 21
2 === 14 days.)
Now A…….14                         3unit
.        B…….21   Lcm 42         2unit
then B joined with A and worked for 5days ==>5*5(3+2) = 25 unit
remaining (42-25)=17unit
then A did that 17 unit alone is 17/3==5 2/3 days.